Binuclear transition metal complexes on gold: Molecular orientation by angular dependent NEXAFS spectroscopy

The influence of the transition metals on the molecular orientation and molecule-substrate interaction has been investigated by angular dependent NEXAFS spectroscopy for the recently synthesised dialkynyl bridged complexes M-2-DEBP (Cl(PBu3)(2)M-C equivalent to C-C6H4[4 C6H4-C equivalent to CM(PBu3)(2)Cl, M = Pt, Pd; DEBP = diethynyl-biphenyl, i.e. C equivalent to C-C6H4-C6H4-C equivalent to C-). Thin films of both samples have been deposited on Au/Si(111), and the angular dependent analysis of the main pi* feature deriving by the superimposition of the resonances due to benzene and acetylene carbon orbitals showed a polarisation effect for Pd-2-DEBP only. A tendency to a preferential molecular orientation at nearly 50 degrees to the surface was calculated. Furthermore, for Pd2-DEBP, the two pi* resonances already assigned to benzene and acetylene carbon atoms showed different angular effects; a likely explanation for this behaviour bear in mind the interaction between sp and sp 2 carbons of the organic DEBP moieties with Pd centres of neighbouring macromolecules, giving rise to interchain interactions then leading to an enhancement of the already assessed self-assembling properties. (C) 2007 Elsevier B.V. All rights reserved.